Mixing apparatus for high pressure fluids at different temperatures



United States Patent O 3,409,274 MIXING APPARATUS FOR HIGH PRESSUREFLUIDS AT DIFFERENT TEMPERATURES Carl W. Lawton, West Hartford, Conn.,assignor to Combustion Engineering, Inc., Windsor, Conn., a corporationof Delaware Continuation-in-part of application Ser. No. 603,007, Dec.19, 1966. This application Nov. 22, 1967, Ser. No. 689,235

7 Claims. (Cl. 259-4) ABSTRACT OF THE DISCLOSURE Mixing apparatus forhigh pressure fluids at different temperatures in the form of aT-connector, wherein the effect of thermally induced stresses on thebody of the apparatus, especially at the intersection of the stem andthe straight portion which is most susceptible to stress, is reduced byproviding the straight portion with an inner liner which defines anannular chamber about the wall of the body into which fluid from thestern is discharged. The body of liquid in the chamber forms a thermalbarrier that prevents the apparatus body from being subjected to unduethermal stresses. Openings in the liner effect passage of fluid from thechamber into the flow stream of the other uid for mixing.

Background of the invention This application is a continuation-impart ofU.S. application Ser. No. 603,007 led Dec. 19, 1966, now abandoned.

The invention relates to Huid mixing apparatus and in particular tomixing vessels wherein two high pressure fluids having substantiallydifferent temperatures can be mixed.

In certain fields, especially the eld of vapor generation, it is oftendesirable t-o mix fluids, each being at substantially differenttemperatures from one another. A particular application is in a vaporgenerator wherein some of the high temperature, high pressure, saturatedliquid from the outlet of the water wall heat exchange surface isrecirculated back through the water walls. Before being readmitted tothe water walls, this liquid must be mixed with lower temperature liquidthat is passed from the economizer. The temperature of the saturatedliquid may be as high as 800 F. while that of the liquid being passedfrom the economizer may be about 500 F. to 600 F. thereby giving rise toa substantial temperature difference, and with it, the problem ofextreme thermal stresses to be encountered by the vessel within whichmixing of these fluids occurs. The magnitude of the thermal stressesgenerated in vessels employed to mix such fluids has heretoforeprevented the use of simple, conventional tube connectors. As analternative, complex, expensive structures had to be employed. One suchstructure is the spherical mixing vessel `shown and described in U.S.Patent No. 3,291,456, issued Dec. 13, 1966, to Deane and assigned to theassignee of the instant application.

Summary of the invention By means of the present invention there isprovided mixing apparatus constructed in the form of a simple T- typefluid connector having a straight portion and interseating stern thatcan be installed in the juncture of the tubes conducting the two uids tobe mixed. Within the apparatus a liner is disposed in concentricrelation to the straight portion of the T and is spaced from the wallthereof so as to form a substantially closed, annular 'ice chamber intowhich fluid flowing from the second fluid inlet defined by the stem isconducted. Openings in the Wall of the liner effect mixing of the twofluids. The body of liquid retained in the annular chamber provides athermal barrier effective to prevent the material forming the apparatusfrom being subjected to undue thermal stressing because of thesubstantial temperature differential imposed by the two uids.Utilization of the apparatus, which is of substantially conventionalform and therefore simple and inexpensive to construct, permits themixing of high temperature, high pressure uids at a fraction of the costheretofore required.

Brief description of drawing FIGURE 1 is a schematic representation of avapor generator incorporating the instant invention;

FIGURE 2 is a sectional view of mixing apparatus according to theinstant invention as applied in the vapor generator of FIGURE l; and

FIGURE 3 is a sectional View of a modified form of mixing apparatusaccording to the invention.

Description 0f the preferred embodiments In FIGURE 1, numeral 10indicates a vapor generator incorporating the present invention. Thevapor generator 10 comprises a feed pump 12, an economizer 14, waterwall heat exchange surface 16 and superheater 18, al1 connected forseries flow. A portion of the fluid emerging from the outlet of thewater wall surface 16 is recirculated, through line 20back to the inletof the water walls where, before being admitted thereto, it is mixed inmixing vessel 22 with fluid flowing from the economizer 14 through line24, and then passed, by means of line 26 and recirculating pump 28 tothe water walls 16.

As shown in FIGURE 2. the mixing vessel 22 comprises a body 30 that isof substantially standard T- connector configuration having a straightportion 32 with two open ends 34 and 36, respectively, and a stem 38disposed at right angles with respect to, and penetrating, the straight32. The ends 34 and 36, and stem 38 are adapted for connection at theintersection of the tubes 20, 24, and 26 by appropriate means such aswelding. In the present arrangement, end 34 of the straight 32 forms theinlet opening for one of the uids being mixed, while end 36 forms theoutlet opening for the mixed Huid. The opening in stem 38 provides theinlet for the second fluid to be mixed. Within the body of the vessel 22is disposed an elongated cylindrical liner 40 extending axially from endto end through the straight 32. The liner 40 is concentrically spacedfrom the-wall of the straight 32 and cooperates therewith to define asubstantially annular chamber 42 that is closed at its ends. The secondfluid inlet defined by stem 38 communicates With the chamber 42 suchthat the chamber is Caused to contain a body of fluid that providesthermal insulation for the metal that forms the body of the vessel 22.

In order to provide for thermal expansion of the liner 40 with respectto the body of vessel 22 it is preferred that it be attached as by meansof welding to the body at one of its ends, here shown as the end 34,while the other end of the liner engages the inner surface of the bodyin sliding contact adjacent the other end 36.

Openings 44 are provided in the wall of the liner 40 to effect passageof the iluid stream entering the vessel through the opening provided bystem 38 into the fluid stream passing through the interior of the liner40 where mixing occurs. The openings 44 are conveniently formed of rowsof circular apertures that penetrate the wall of the liner. In order toobtain better -mixing of the fluids, the openings 44 are provided aboutthe full circumference of the liner wall and may, as shown in FIGURE 2,be inclined in the direction of ow of fluid through the liner in orderto somewhat reduce the amount of pressure drop experienced by the fluidin flowing through the apparatus. Where, however, more pressure drop canbe tolerated or where better mixing is desired, it is recommended thatthe openings be radially projected through the liner wall in order thatsome turbulence be effected within the liner to promote mixing.

For best results it is further recommended that the total crosssectional area of the holes 44 should be less than half the flow crosssection of the inlet branch 38, most preferably appr-oximately 35% ofthe flow cross section of the latter. In this manner, the fluid jetscreated by the fluid flowing through the openings 44 from the nozzle 38will penetrate the body of liquid flowing through the straight portion32 between the inlet and outlet ends 34 and 36 to a sufficient depth toobtain abundant mixing.

According to the invention, the openings 44 are provided only in thataxial portion of the liner 40 that is adjacent the fluid inlet definedby the stem 38. The remainder of the liner wall on both sides of theapertured portion is fluid impervious in order to create areas of lowfluid velocities in the adjacent portions of the chamber 42. Bymaintaining low fluid velocities within the chamber 42 the body ofliquid contained therein is caused to operate as a thermal barrier for,as the velocity of the fluid within the chamber decreases, itstemperature Will tend to assume that of the fluid entering the liner 40through the first fluid inlet opening 34. Since the velocity of thefluid in the chamber 42 decreases axially along the length of thestraight 28 to the end of the chamber, its temperature will thereforetend more and more to that of the fluid flowing through the liner withthe maximum effect being realized at the end of the chamber where thefluid velocities are at a minimum. Thus the temperature of the materialthat forms the apparatus will experience only gradual temperaturegradients along the length of the straight and therefore, thermalstresses within the member can be maintained within tolerable limits.Moreover, because the fluid velocity in the chamber 42 is greatestadjacent the second fluid inlet defined by the intersecting of the stem38 and straight 32 which is the area most susceptible to stress, thetemperature gradient in this area will be minimized thereby eliminatingthe danger of material failure at this point.

The operation of the present invention is described with reference toits use in the vapor generator organization shown in FIGURE l where thefluid being passed through line 20 may be of the order of 800 F. andthat emerging from the economizer 14 and passed through line 24 is about600 F. The mixing vessel 22 is installed at the intersection of lines20, 24, and 26 with its first fluid inlet end 34 connected to line 20,its miXed fluid outlet end 36 connected to line 26 and its stem 38forming the second fluid inlet connected to line 24. The cooler (600 F.)liquid therefore is caused to pass through the interior of liner 36along the length of the straight 32 while the hot (800 F.) recirculatedliquid entering through stem 38 is passed to the annular chamber 42filling the same to form a thermal barrier along the length of thestraight 28. The hotter liquid is caused to pass through the openings 44in liner 40 from the chamber 42 into the interior of the liner where itis mixed with the cooler liquid and flows out the mixed fluid outlet 36into line 26. Within the chamber 42 the temperature of the hotter liquidtends to decrease along the lengthl of the chamber from the innersection of the stem 38 to the ends thereof. Since this liquid gives upheat to the cooler fluid and thereby assumes a temperature intermediatethat of the two liquids being mixed, it acts as a thermal shield for thewall of the straight thus preventing direct contact of the hightemperature fluid with the body. Because of the presence of the thermalshield and because the openings in the liner 40 which produce thehighest liquid velocities within the chamber 42 are located in the areaof the inner section of the stern 38 with the straight 32 thetemperature gradient at this point, which is the most susceptible tofailure, is at a minimum. Furthermore, because the temperature of theliquid within chamber 42 gradually decreases from this point to the endsthereof the metal temperatures experienced by the body of the straightgradually decrease along the length of the body 30 such that thetemperature gradient at any point is slight. The result therefore isthat the simple T-connection can be ernployed to mix high pressureliquids having different temperatures without danger of stressing thematerial beyond tolerable limits.

Although the invention has been described with reference to anapplication wherein the cooler of the fluids being mixed is caused t-oenter the inlet 34 with the hotter fluid entering the inlet 38 it shouldbe understood that the apparatus will operate equally as well when thefluids admitted to the two inlets are reversed, i.e. with the hotterfluid being admitted to the inlet 34 and the cooler fluid to inlet 38.

In FIGURE 3 there is shown a somewhat modified application of thepresent invention. In this arrangement the liner indicated as numeral40' is formed with a venturi constriction located adjacent theintersection of the stern 38 and the straight 32. Openings 44', hereshown as being radial, are disposed about the circumference of the linerin the constricted portion thereof. By employing a liner so formed thefluid pressure at the constriction is reduced so as to enhance the entryof fluid flowing from the chamber 42 into the interior of the liner inorder to promote mixing thereof. In this modification there are alsoshown annular baffle members 46 disposed in the annular chamber 42between the walls of the liner 40 and vessel body 22. Openings 48 areprovided in the bales such that some fluid circulation therethrough canoccur.

By means of these baflle members the liner 40' is provided with lateralstructural support for maintaining it in spaced relation from the wallof the body 30. Moreover, the presence of these bafile members alsopromotes fluid stagnation in the remote ends of the chamber 42 betweenthe external surface of the liner 40 and inner surface of the -body 30.Thus, the tendency of the fluid residing in the remote portions of thechamber 42 to assume the temperature of the fluid flowing in theadjacent portion of the interior of the liner is increased therebyfurther reducing the thermal gradients along the length of the vesselbody 30.

It is particularly recommended that, in a mixing vessel of the typedisclosed in this embodiment wherein the line 40 is formed with aventuri constriction adjacent the inlet opening formed by the stem 38,that the flow area presented by the openings 44 be limited to less thanhalf, and ideally about 35%, that presented by the internal diameter orthe stem 38. To so limit the flow area through the liner wall insuresadequate penetration of the stream of fluid flowing axially of the linerby that entering through the openings. In this manner complete mixtureof the two fluids through the entire transverse area of the linerinterior is enhanced.

It will be understood that various changes in the details, materials andarrangements of parts which have been herein described and illustratedin order to explain the nature of the invention, may be made by thoseskilled in the art within the principle and scope of the invention asexpressed in the appended claims.

What I claim is:

1. In a vapor generator having tubulous heat exchange means for theheating of fluid by the indirect exchange of heat from a heating medium,means for passing fluid to be heated through the tubes of said heatexchange means, and means for withdrawing a portion of the heated fluiddownstream of said heat exchange means and for recirculating 4saidheated fluid therethrough in mixed relation with said fluid to beheated, apparatus for mixing said fluids comprising:

(a) a vessel body having an open ended straight portion and an angularlydisposed, hollow stem penetrating the wall of said straight portionintermediate the ends thereof, one end of said straight portion formingan inlet for one of said iluids to be mixed and the other end forming amixed uid outlet, said stem forming an inlet for the other of said uids;

(b) means forming a liner disposed within the straight portion of saidvessel in spaced relation from the wall thereof to form a substantiallyclosed annular chamber extending between the ends of said straightportion and communicating with the inlet for-med by said stem;

(c) means forming openings in the wall of said liner adjacent the locusof penetration of said stem, the remainder of said liner wall beingfluid impervious.

2. Apparatus as recited in claim 1 wherein the flow area presented bysaid openings is less than half that presented bythe internal diameterof said stem.

3. Apparatus as recited in claim 2 wherein the ilow area presented bysaid openings is substantially thirty-five percent that presented by theinternal diameter of said stem.

4. Apparatus as recited in claim 2 wherein said liner contains a venturiconstriction adjacent the locus of penetration of said stem.

5. Apparatus as recited in claim 4 wherein said openings arecircumferentially spaced around the constricted portion of said liner.

6. Apparatus as recited in claim 4 including:

(a) annular bafe members spacedly supporting said liner with respect tothe inner surface of the straight portion of said vessel, said bathemembers being disposed on opposite sides of the locus of penetration in:spaced relation from the ends of said chamber; and

(b) means forming openings through said baie members for passing uidtherethrough.

7. Apparatus as recited in claim 1 wherein said liner is fixedlyattached to the wall of said vessel adjacent one end thereof and insliding contact with said wall at the other end thereof.

References Cited UNITED STATES PATENTS 1,784,503 12/1930 Swann 259--1511,848,122 3/1932 Forster 259-151 2,577,664 12/1951 Pro 259-151 ROBERT W.JENKINS, Primary Examiner.

